Effect of nanoparticle type on prebreakdown and breakdown characteristics of transformer oil

In order to reveal the effects of nanoparticle type on breakdown and prebreakdown characteristics, this paper presents an experimental study on the effects of conductive Fe
3
O
4
nanoparticles, semi-conductive TiO
2
nanoparticles and insulating Al
2
O
3
nanoparticles on the breakdown strength and prebreakdown streamer propagation in transformer oil under positive lightning impulse voltage. Nanoparticle with the same size, modifier and concentration are prepared. The results indicate that the type of nanoparticles has a notably effect on breakdown voltage of transformer oil. Positive breakdown voltage of Fe
3
O
4
nanofluid is markedly increased by 41.3% compared to that of pure oil. Followed by TiO
2
nanofluid, the breakdown voltage is increased by 29.8%. Whereas for Al
2
O
3
nanofluid, it is slightly increased by 7.4%. Moreover, streamer structure, propagation length and velocity in pure oil and nanofluids were investigated using the shadowgraph technique. It is demonstrated that streamer propagations are changed in different extent with the presence of three types of nanoparticle. In Fe
3
O
4
and TiO
2
nanofluids, streamers with more branches have lower velocity than that in pure oil. Whereas in Al
2
O
3
nanofluid, streamers are similar to that in pure oil. The propagations of positive streamers in the nanofluids are notably suppressed by Fe
3
O
4
and TiO
2
textbf nanoparticles, leading to the improvements of breakdown strength. The nanoparticle effect on streamers is further confirmed by simulation.